In the field of semiconductor device production, such as of IC (integrated circuit) or LSI (Large Scale Integration), a ceramic holder has been used for holding and positioning a semiconductor wafer in a production apparatus. Since the wafer is treated at a high temperature in the apparatus, a sintered alumina-based ceramic has been used for the material of said holder.
In the process of wafer treatment, particularly in a diffusion process for developing complicated circuit patterns on the wafer, a very high accuracy of wafer positioning is required, so that the wafer holding surface of said holder should be precisely finished by polishing, grinding or other machining. However, the alumina-based ceramic as a conventional material for such holder is very dense and tough, so that the machining thereof is generally very difficult and causes an increase in the production cost. Such problem that the increase in the machining cost directly leads to a price-raise of the products frequently occurs not only for the wafer holder, but also for other alumina-based ceramic products, such as sliding parts.
In order to enhance the efficiency of the ceramic-machining, it seems effective to use a porous sintered alumina ceramic as the material for said parts instead of a dense alumina ceramic however, for ceramic parts such as the wafer holder used under a high vacuum atmosphere, the porous ceramic is not suitable since water or other molecules adsorbed in the open pores are discharged during the evacuation, thereby preventing the atmosphere from reaching to sufficient degree of vacuum.
The object of this invention is to offer a sintered alumina-based ceramic and a sintered alumina-based ceramic part which exhibit good machinability despite of having high density, thereby being suitable for a parts used under a high vacuum atmosphere, such as of semiconductor treatment.